This invention relates generally to check valves and more particularly to a spring check valve cartridge for use with diaphragm pumps and the like and more particularly where a compact reversible flat check valve requiring minimal depth is desired.
Pumps using check valves to control flow through the pump generally rely on gravity for the checks to function particularly when there is no fluid in the pump.
The type of checks used are either a ball or a flat/disk type. They allow flow in one direction and prevent flow in the opposite direction. In a typical pump there are two checks, one on the pump inlet and one at the outlet. The inlet check allows fluid to enter the pump when a vacuum is pulled in the pumping chamber. At the same time the outlet check is closed preventing fluid or gases to enter the pumping chamber during the suction cycle. When the pump expels the fluid, the inlet check closes due to gravity and frictional drag between the check and the fluid being pumped. The outlet check is forced open due to pressure acting on the check which was generated in the pumping chamber. The cycle begins again at the end of the pumping stroke. For this type of pump to self prime the pump must be oriented such that gravity will cause the checks to seat properly.
One method used to overcome this limitation in the prior art is to use a mechanical spring to physically force the check against the seat. The arrangement works well in most cases; however, the spring is subject to fatigue failure if the pump operates at high cycle rates. Full flow rate is also reduced because the spring limits the check lift. The volume occupied by the spring loaded check is larger. Free springs may cause problems during assembly and the added volume of the check reduces the pumps' volumetric efficiency and increase the net positive suction head required for the pump to begin to operate.
The check valve feels only the difference between suction pressure and the pressure in the fluid chamber. When the pressure differential is sufficient to lift the check from its seat, the valve will begin to open. The rate of pressure drop when the pump piston or diaphragm creates a vacuum is a function of the volume ratio and the vapor pressure of the fluid pumped. Loading the check with a spring requires the pump to generate higher suction pressure in the pumping chamber to open the check.
Metallic springs cannot be used in environments where chemical compatibility between the spring and the process fluid will result in corrosion of the spring. In addition, the form of the spring may create instability in the ability of the check to seat by applying non-union or offset pressure in the direction of seating.
Other well-known forms of check valves, such as Duckbill or umbrella checks, utilize elastomeric materials which limit their use as to the type of fluids pumped and are subject to damage or being sucked inside out at high flow rates and/or high back pressure.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully described hereinafter.